very briefly:
there is an active voice and a passive voice.
In the passive voice, the subject of the sentence 'undergoes' (in need of another word) the action of the verb.
e.g. Bob got hit by a car yesterday.
In this case, Bob 'undergoes' the action of the car hitting him.
In an active voice, the subject does not 'undergo' the action, put likely performs it.
e.g. A car hit Bob yesterday.
In a passive voice, either the verb 'to be' or 'to get' is used.
All I know by heart right know
![Smile [:)]](/emoticons/emotion-1.gif)
Passed my grammar test though :P